Sarcasm is an open lie. Is it not? Sarcasm is the opposite of the truth for the purpose of humor.
Sarcasm is insincere in order to make a point. For instance, to issue an agreement with someone to a ridiculous degree, or to agree in such a way that makes the recipient of the comment understand that the person does not really agree, and that they really believe that to agree with such is actually quite ridiculous.
Granted, it is insincerity at its core, but its intent is
NOT to deceive. On the contrary, the intent is to display the REAL truth as it is felt by the person employing sarcasm, and to get the recipient to feel and understand more the opinion of the person using the sarcasm.
Sometimes stating things plainly simply does not work. Sometimes people simply
need to be mocked in order to understand and feel how ridiculous they make themselves appear.